Question

Ozone is formed in the upper layer of the atmosphere from oxygen by the action of: (a) Cosmic rays (b) Ultraviolet rays (c) Free radicals (d) Nitrogen oxides

Short answer

Ozone is formed from oxygen by the action of ultraviolet rays.

Step-by-step solution

Understanding the Components

We need to understand where ozone formation occurs and what elements or conditions are involved in this process. Ozone is formed only in the upper layers of the atmosphere, specifically in the stratosphere, largely due to the presence and action of specific rays or particles.

Identify the Role of Ultraviolet Rays

Ultraviolet (UV) rays, which are part of the sunlight that reaches the Earth's atmosphere, play a crucial role in breaking down molecular oxygen ( O_2 ), creating individual oxygen atoms that can recombine to form ozone ( O_3 ). This process, called photodissociation, is a key step in the formation of ozone in the stratosphere.

Linking the Explanation to the Options

Given the multiple-choice options, we evaluate each one for its relevance to ozone formation. While cosmic rays and free radicals are parts of different atmospheric processes, and nitrogen oxides are involved in the depletion of ozone rather than its formation, it is ultraviolet rays that provide the energy needed for the production of ozone.

Key concepts

Stratosphere

The stratosphere is a crucial layer of Earth's atmosphere, situated above the troposphere and below the mesosphere. It extends from approximately 10 to 50 kilometers above the Earth's surface. This layer contains the majority of our planet's ozone, hence sometimes referred to as the "ozone layer." Understanding the stratosphere is vital because it plays a significant role in protecting life on Earth.

• It absorbs most of the Sun's harmful ultraviolet radiation, which can cause skin cancer and cataracts in humans.
• The ozone in the stratosphere also helps regulate the temperature of our planet by interacting with radiation from the Sun.

The overall stability of the stratosphere, with its relatively minimal air turbulence compared to the troposphere, provides an ideal environment for ozone formation and accumulation. The production and destruction of ozone within this layer are crucial parts of atmospheric chemistry.

Ultraviolet Rays

Ultraviolet (UV) rays are a form of electromagnetic radiation emanating from the Sun. These rays have wavelengths shorter than visible light but longer than X-rays, which makes them particularly energetic.

• UV rays are essential for the formation of ozone in the Earth's atmosphere.
• They possess the energy required to break the bonds of molecular oxygen ( O_2 ), a process necessary for creating ozone.

There are three types of UV radiation:

• UVA (long-wave): Closest to visible light.
• UVB (medium-wave): Can cause sunburn and has various effects on human health.
• UVC (short-wave): Most energetic and completely absorbed by the atmospheric ozone.

In the context of ozone formation, UVB and UVC play pivotal roles by initiating the photodissociation of molecular oxygen, leading to the creation of individual oxygen atoms that eventually form ozone.

Photodissociation

Photodissociation is a fundamental process in atmospheric chemistry, particularly in the context of ozone formation. This term refers to the breaking down of a chemical compound by photons, specifically from sunlight.

• In the stratosphere, photodissociation involves the splitting of molecular oxygen ( O_2 ) by ultraviolet light.
• This initiates a chemical reaction chain crucial for producing ozone ( O_3 ).

When UV light hits molecular oxygen, the energy from the light breaks the bond between the two oxygen atoms. As a result, individual oxygen atoms are freed, which can then react with other O_2 molecules to form ozone. This mechanism ensures a continuous supply of ozone in the stratosphere, maintaining the critical balance needed to protect our planet from excessive ultraviolet radiation. The equilibrium between ozone creation and destruction is a primary focus of atmospheric scientists.

Atmospheric Chemistry

Atmospheric chemistry is dedicated to understanding the composition and reactions of chemical entities in the Earth's atmosphere. It encompasses a wide range of processes, from natural phenomena to human-induced changes.

• The formation and destruction of ozone are central topics within this field.
• Ozone not only forms a protective layer in the stratosphere but also has roles near the Earth's surface, where it can act as a pollutant.
• Anthropogenic activities, like emissions of chlorofluorocarbons (CFCs) and other pollutants, have significant impacts on atmospheric chemistry.

The study of atmospheric chemistry involves assessing how various chemical processes affect climate, air quality, and health. Given that human actions have altered the balance of natural atmospheric chemistry, understanding these changes is critical. Specialists work on policies and technologies to mitigate negative impacts, striving for a sustainable and healthy atmosphere for all living beings.